1. Field of the Invention
The present invention relates to an air bag device to be mounted on a vehicle, and particularly to an air bag device in which a folded air bag is enclosed by a sheet for preventing the air bag from unfolding when in a non-deployed state.
2. Description of Related Art
Conventionally, an air bag device, for example, an air bag device for an assistant seat was constituted by an air bag accommodated in a folded state, an inflator for supplying expansion gas to the air bag, a casing for receiving and holding the air bag and the inflator, and a cover for covering the folded air bag. The folded air bag was accommodated in the casing and enclosed within a sheet for preventing the air bag from unfolding when in a non-deployed state (see JP-A-10-315889).
The sheet disclosed in the above publication was a material used to enclose the folded air bag so that the air bag was not restored to an unfolded state when the air bag device having the air bag accommodated in the casing was assembled. Further, this sheet had a breakable portion formed by slits so that the sheet was ruptured in case of development and expansion of the air bag against the passenger. While being formed to be offset from the center to the left and right edges of the sheet respectively, the slits were arranged uniformly on the left and right sides of the sheet, so that the air bag could be developed faster on the left and right sides of the sheet than the center side in the vehicle, and developed and expanded in a large area against the passenger in case of development and expansion of the air bag.
In the above air bag device, however, if during deployment the air bag interfered with a passenger sitting in a normal position, the pressing force against the passenger per unit area could be reduced because the air bag interfered with the passenger across a large area. There was however room for improvement in reducing the total pressing force of the air bag against the passenger.
It is an object of the present invention to provide an air bag device in which the pressing force against a passenger in case of development and expansion of the air bag can be reduced even when the passenger sits in a normal position.
According to the present invention, there is provided an air bag device constituted by: an air bag which is folded and accommodated; a sheet for enclosing the air bag in a folded state so as to prevent the unfolding of the airbag; a regulation wall portion formed by the sheet and covering a surface of the air bag on a side from which the air bag projects in case of expansion of the air bag; and a breakable portion provided in the regulation wall portion so that the breakable portion can be ruptured while being pushed by the air bag in case of the expansion; wherein the breakable portion is disposed so as to be ruptured from one of circumferential edge sides of the regulation wall portion.
Preferably, the breakable portion is disposed so that the breakable portion is ruptured from a left or right edge side of the regulation wall portion mounted on a vehicle when the air bag is expanded.
In this case, preferably, the breakable portion is formed by a slit provided in the regulation wall portion, the slit being offset to the left or right edge side which is a rupture initiation side.
Further, in this case, preferably, the folding of the air bag is completed when folded portions of the air bag extending in the left-right direction are folded and superimposed onto a center part of the air bag, and one of the left folded portion and the right folded portion, as a rupture initiation side in the regulation wall portion, is folded and superimposed on the other one of the left folded portion and the right folded portion.
Further, in this case, preferably, the sheet is provided with an auxiliary wall portion which is connected to the regulation wall portion and which covers a surface of the air bag on a side perpendicular to the side from which the air bag projects, and the auxiliary wall portion is connected to an edge side of the regulation wall portion in opposition to the rupture initiation side.
In the air bag according to the present invention, the regulation wall portion of the sheet is disposed to cover a surface of the air bag on the side from which the air bag projects in case of expansion of the air bag, and the breakable portion is disposed in the regulation wall portion so as to be ruptured from one of the circumferential edge sides of the regulation wall portion. Therefore, the air bag in the initial stage of development and expansion does not project from the center of the regulation wall portion but projects from one of the circumferential edge sides of the regulation wall portion which is the rupture initiation side, while the folding of the air bag is canceled. On this occasion, the air bag projects in the condition that the folding of the air bag on the side opposite to the rupture initiation side in the breakable portion has not been cancelled yet, so that the air bag projects not against the passenger but in a bent state so that the air bag is pulled toward the side opposite to the rupture initiation side in the breakable portion.
Therefore, even if the passenger sits in a normal position, the air bag in the initial stage of development and expansion projects in a bent state toward the right or left side of the passenger, that is, the air bag projects so as to avoid directly impacting the passenger. Thus, the air bag does not impose large pressing force on the passenger sitting in a normal position.
Of course, in the case where the passenger sits in the proper or normal position, the air bag expands toward to the passenger after rupture of the breakable portion in the regulation wall portion is completed and the air bag is fully deployed. Hence, the air bag can restrain the passenger accurately in the condition that the development and expansion of the air bag is completed.
Accordingly, in the air bag device according to the present invention, even if the passenger sits in the normal position, the pressing force against the passenger at the time of development and expansion of the air bag can be reduced. Further, the member providing the operations and effects as described above is a constituent component of the background-art air bag device, that is, the sheet for preventing the air bag from unfolding when in a non-deployed state so that the air bag device according to the present invention can be produced very conveniently.
Preferably, if the breakable portion of the regulation wall portion is disposed so as to be ruptured from the left or right edge side of the regulation wall portion mounted on the vehicle when the air bag is expanded, the air bag in the initial stage of the development and expansion projects toward the right or left side of the passenger seating in front of the normal position so as to avoid directly impacting the passenger, so that the fear that the air bag interferes with the passenger can be reduced compared with the case in which the air bag projects toward the upper side rather than toward the passenger.
In this case, if the breakable portion is formed by a slit offset to the left or right edge side, which is the rupture initiation side, of the regulation wall portion, the slit is simply disposed in the regulation wall portion so that the breakable portion can be formed easily by forming a rift by a cutter or the like, in comparison with the case where the breakable portion is formed by stitching by use of threads or the like.
Further, the folded portion folded and superimposed on the upper side projects first when the air bag is developed and expanded. At that time, the folded portion folded and superimposed on the upper side is ruptured rapidly from the rupture initiation side of the regulation wall portion. Thus, the mode in which the air bag projects from one of the circumferential edge sides of the regulation wall portion in a bent state so as to avoid directly impacting the passenger can be ensured.
Still further, if the sheet is provided with an auxiliary wall portion which is connected to the edge side opposite to the rupture initiation side in the regulation portion and which covers a surface of the air bag on the side perpendicular to the side from which the air bag projects, the air bag is restricted by the auxiliary wall portion in the initial stage of development and expansion so as not to project toward the side opposite to the rupture initiation side in the regulation wall portion, and the mode in which the air bag projects from one of the circumferential edge sides of the regulation wall portion in a bent state so as to avoid directly impacting the passenger can be ensured.
Furthermore, in the air bag device, the sheet may be provided as a woven cloth with a lattice pattern. The woven cloth may be oriented so as to form a bias angle with respect to the breakable portion formed as a slit.